1. Field of the Invention
This invention relates to a focal plane shutter for cameras.
2. Description of Related Art
Focal plane shutters for cameras which are recently publically known include: focal plane shutters each of which is provided with one shutter blade unit; and focal plane shutters each of which is provided with two shutter blade units called a first blade unit and a second blade unit respectively. En the both cases, these shutter blade units have the same fundamental structure, and each of the shutter blade units consists of: two (or rarely three) arms one end of each of which is rotatably fitted to a shutter base plate; and a plurality of blades which are rotatably supported through connection shall members toward the other end (free end) of each of the two arms in turn. (However, some shutter blade units rarely include only one blade.) Also, each of the shutter blade units is made to open and close an exposure aperture by a blade unit-driving unit, and the blade unit-driving unit is usually formed in such a way that: the blade unit-driving unit is fitted to the shutter base plate and can be rotated in a reciprocating manner; its driving pin is connected to one of the arms of the shutter blade unit; and the blade unit-driving unit is rotated in one direction by the elastic force of a driving spring when shooting is performed.
Also, in focal plane shutters each of which is provided with two shutter blade units, not only a focal plane shutter which includes first blade unit-driving and second blade unit-driving units in ones, but also a focal plane shutter disclosed in Japanese Patent KOKAI No. 2007-298544 is publicly known. The focal plane shutter disclosed in Japanese Patent KOKAI No. 2007-298544 is formed in such a way that: only the first blade unit-driving unit of two blade unit-driving units is composed of two driving members which are rotatably fitted to the same shall; the first driving member of the two driving members is provided with the above-described driving pin; and the second driving member of the two driving members is connected to the above-described driving spring, so that the second driving member presses the first driving member to rotate the first driving member when the second driving member is rotated by the elastic force of the driving spring in exposure operation.
In addition, a focal plane shutter disclosed in Japanese Patent KOKAI No. 2001-305605 is also publicly known in focal plane shutters each of which is provided with two shutter blade units. The focal plane shutter disclosed in Japanese Patent KOKAI No. 2001-305605 is formed in such a way that: only the second blade unit-driving unit of two blade unit-driving units is composed of two driving members which are rotatably fitted to the same shaft; the first driving member of the two driving members is provided with the above-described driving pin; and the second driving member is connected to the above-described driving spring, so that the second driving member presses the first driving member to rotate the first driving member when the second driving member is rotated by the elastic force of the driving spring in exposure operation.
Now, these shutter blade units for focal plane shutters operate at extremely high speed in shooting and meet stoppers to be stopped on completion of the operation. Accordingly, if any countermeasures for this are not taken, the shutter blade units inevitably break or bounce large due to the impact of the stoppers against the shutter blade units. And, the large bounces of the shutter blade units cause such a disadvantage as the shutter blade units inevitably cover a part of an exposure aperture temporarily in the case where the shutter blade units operate to open the exposure aperture or as the shutter blade units inevitably open a part of the exposure aperture temporarily in the case where the shutter blade units operate to close the exposure aperture. Accordingly, up to now, various methods for braking the shutter blade units have been taken in order to brake the movements of the shutter blade units directly or indirectly at the stage just before the completions of the operations of the shutter blade units in shooting, or buffer members which are made of rubber are fixed to the stoppers in order to buffer the impact in the stops of the operations of the shutter blade units.
Also, the methods for braking the shutter blade units are roughly divided into: a method of braking the shutter blade units by making braking means directly come into contact with the blade unit-driving units; a method of braking the shutter blade units by making braking means directly come into contact with connection shafts connecting the arms and the blades; and a method of braking the shutter blade units by making braking means directly come into contact with blades. And, one of these methods is used solely or these methods are used together with each other. In these methods for braking the shutter blade units, general constitutions for the method by making braking means directly come into contact with the blade unit-driving units include a constitution in which: a brake member is rotatably fitted to a shutter base plate; and the above-described driving pin is made to meet the brake member at the stage just before the completions of the operations of the shutter blade units in shooting, to rotate the braking member against friction force caused by a friction-providing means (plate spring or friction plate).
Japanese Utility Model KOUKOKU No. HEI 6-24826 discloses one example of the constitution including only one such brake member, and Japanese Patent KOKAI No. 2010-8647 discloses one example of the constitution in which a coil spring is connected to the brake member while the constitution disclosed in Japanese Utility Model KOUKOKU No. HEI 6-24826 is being used. However, it is possible to achieve a braking effect even if the coil spring is merely connected to the braking member without providing a friction-providing means. And, this kind of constitution can be used both for the above-described focal plane shutters provided with one shutter blade unit and for the above-described focal plane shutters provided with two shutter blade units. Also, this kind of constitution can be also used for a focal plane shutter which is disclosed in Japanese Patent KOKAI No. 2007-298544 or in Japanese Patent KOKAI No. 2001-305605 and in which the first blade unit-driving unit or the second blade unit-driving unit is composed of two driving members.
In addition, in the case where a focal plane shutter provided with two shutter blade units is used, this kind of braking mechanism may be used for the blade unit-driving unit for each of the two shutter blade units, as disclosed in Japanese Patent KOKAI No. 2010-8647. Alternatively, focal plane shutters may be formed in such a way that one another kind of braking means or a plurality of another kinds of braking means as described above are used only for one of the two shutter blade units and this kind of braking mechanism is used only for the blade unit-driving unit for the other of the two shutter blade units. The present invention relates to a focal plane shutter for cameras which is provided with a braking mechanism including at least one braking member and in which the braking member is rotated by a driving pin of a blade unit-driving unit, as described above.